Automated Dilutions Using the Centurion Autosampler

Importance of the Topic

Accurate determination of volatile organic compounds (VOCs) in environmental samples often requires dilution of ‘‘hot’’ samples to bring analyte levels within calibrated ranges. Manual dilutions are labor-intensive, prone to error, and risk sample integrity due to vial opening and loss of volatiles. Automated dilution on an autosampler can streamline workflows, reduce errors, and preserve sample fidelity.

Study Objectives and Overview

This study evaluates the performance of the EST Analytical Centurion WS autosampler equipped with a syringe dilution option capable of preparing dilutions from 2× to 400×. The goals were to assess precision and accuracy of multiple dilution factors against a 50 ppb reference standard, and to demonstrate linearity by generating a nine-point calibration curve via automated serial dilutions spanning 0.5 ppb to 200 ppb.

Methodology

Field-relevant standards were prepared at 50 ppb final concentration by performing four replicate injections for each dilution factor: 2×, 5×, 10×, 50×, 100×, 200×, and 400×. Blanks were run between replicates. A manual nine-point calibration curve (0.5–200 ppb) established baseline instrument response. Linearity of automated dilutions was assessed by serially diluting a 200 ppb standard in nine 40 mL vials using the autosampler syringe.

Used Instrumentation

• Autosampler: EST Centurion WS with syringe dilution option
• Purge-and-Trap Concentrator: EST Encon Evolution with Vocarb 3000 trap
• Gas Chromatograph/Mass Spectrometer: Agilent 7890A/5975C inert XL
• Column: Rxi-624Sil MS, 30 m × 0.25 mm × 1.4 μm film
• Carrier Gas: Helium at 1.0 mL/min

Main Results and Discussion

Precision across all dilution factors averaged below 5 %RSD up to 50× and remained under 8 %RSD at the highest 400× dilution. Accuracy of replicates fell within 90–110% of the target 50 ppb standard for most compounds. Automated nine-point calibration yielded average response factor %RSD below 10%, demonstrating robust linearity from 0.5 ppb to 200 ppb. Chromatogram overlays confirmed retention time consistency and peak integrity across serial dilutions.

Benefits and Practical Applications

• Minimized manual handling reduces calculation errors and exposure risks.
• Sealed-vial operation preserves volatile analytes and improves data reliability.
• Broad dilution range (2×–400×) supports diverse environmental sample concentrations.
• Automated curve generation accelerates workflow and ensures reproducible calibration.

Future Trends and Opportunities

Integration of advanced autosampler dilution schemes with real-time data feedback could enable adaptive calibration and dynamic range extension. Combining autosampler dilution with on-line sample preparation modules or microfluidic devices may further reduce sample consumption and improve throughput in high-volume environmental and industrial laboratories. Development of software algorithms to optimize dilution sequences based on preliminary sample screening will enhance efficiency.

Conclusions

The Centurion WS with syringe dilution demonstrates high precision (<5 %RSD) and accuracy (90–110%) across a wide dilution range. Automated calibration curve preparation produced consistent response factors (%RSD <10%). Adoption of this automated dilution approach can improve laboratory efficiency, reduce human error, and maintain sample integrity in volatile compound analysis.